The importance of twin studies in determining the causation of a disease problem is to help separate genetic and environmental risk factors. The Virginia Twin Registry, the only active population-based registry of twins in the United States, and the Norwegian Twin Registry were developed in a parallel fashion. Both cover about the same time period and have gathered data on each population using the same instruments. The estimated number of ulcerative colitis (UC) twin pairs (one or both reporting a diagnosis of UC) available from both registries is 130. An estimated 12-15 Crohn's disease (CD) twin pairs are so identified. A large amount of medical and family history information on first degree relatives and a questionnaire used to determine zygosity have already been collected from members of these registries, if married, their spouses, and offspring. Thus three generations of persons can be studied with respect to the occurrence of inflammatory bowel disease (IBD). The analysis will be based on data already available as well as new information to be collected as a part of this study. Medical records relevant to the diagnosis of UC or CD will e abstracted to confirm each case against established diagnostic criteria. Data will also be collected which will determine the time frame relationship between the date of diagnosis and exposure for factors of interest. The primary factors to be examined in the study are twin pair and 'lifestyle' characteristics and medication useage. The analysis will determine the concordance for IBD among mono- and dizygotic twins, which will allow testing of simple genetic hypotheses in the population of available cases. Factor analysis will be limited to UC cases. Factors which differ between cases and co-twins members of a twin or between twins and theirs spouses may identify 'lifestyles' characteristics or medications related to increased or decreased risk. In addition, the occurrence of UC and a comparison of characteristics between twins' and spouses' families will be examined. Because of the limited number of cases, CD pairs will only be examined descriptively. This proposal is intended to be a feasibility study of confirming the diagnosis of UC and CD among twin cases. In addition, we intend to test simple genetic hypotheses among twins and to explore in a preliminary fashion hypotheses about factors relevant to IBD risk.